docs(init): validate specification — v1.23 milestone (REQ-263..275)

Established active_milestone: v1.23 (Nova Deck Cleanup & Python PPTX).
NFR milestone (docs/render/test only; no features). Tags on v1.22.x line
(v1.22.0 P0 -> v1.22.6 P6 final = milestone release). Branch:
milestone/v1.23-deck-cleanup-python-pptx.

Added REQ-263..275 to REQUIREMENTS.md covering:
- Consolidate docs: single -marp.md source of truth, delete plain .md,
  speaker notes/talking points as Marp HTML comments, keep
  talking-points.md as synced standalone aid (REQ-263,264)
- Restore clean style: theme:default + inline style block (S&P palette),
  retire nova-sp-theme.css from render (keep as reference), benefit
  callout restyle (REQ-265,266,267)
- Inline images: scripts/inline_images.py for self-contained
  redistributable HTML (REQ-268)
- Python PPTX generator: scripts/render_pptx.py structured editable
  S&P-themed PPTX via python-pptx, both PPTX outputs produced + attached
  (REQ-269,270)
- Trim word count: targeted ~20-30% trim on verbose slides, remove
  'penetrate' term (REQ-271,272)
- CI/tests/README: workflows install python-pptx, tests updated,
  README rewritten (REQ-273,274,275)

Driven by user feedback: deck looked 'out of whack'; wanted to return to
the clean style of the old the-developer-experience.html. Investigation
revealed the 'clean' reference was itself MARP output (default theme +
inline style); the standalone nova-sp-theme.css approach was fragile.

---ci---
project: acdl
phase: 0
milestone: v1.23
status: specify
---/ci---

.ciagent/config.json

@@ -8,7 +8,7 @@
   ],
   "active_project": "acdl",
   "active_projects": ["acdl"],
-  "active_milestone": "v1.22",
+  "active_milestone": "v1.23",
   "autonomy": {
     "level": "full",
     "escalation_hooks": ["deploy", "delete_data", "merge_to_main"],